DNS

Clean DND cache

Windows 環境下

ipconfig /flushdns

Mac OSX 環境下

dscacheutil -flushcache

Linux 環境下

/etc/init.d/nscd restart

MxToolbox

All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool. Input a domain name or IP Address or Host Name. Links in the results will guide you to other relevant tools and information. And you'll have a chronological history of your results.